This invention relates to film cassettes.
The modern automatic camera comprises a large number of features which require a battery to operate them. Of these the feature which requires the most power is the automatic winding of the film out of the cassette, a frame at a time. To pull a frames' length of film out of the cassette it is required to overcome considerable frictional inertia and this is a heavy drain on the battery. In fact, often an automatic camera is rendered inoperable in the middle of exposing a length of film as the battery has become used up and usually there is no manual film drive mechanism. Thus, in order to reduce the drain on a battery in an automatic camera it would be advantageous to reduce the inertial friction encountered when winding the film out of the cassette.
It is thought that the three main causes of the friction encountered when winding a film out of a cassette are:
(a) the friction caused by pulling the film past the velvet light seals which form light sealing lips in the film exit slot of the cassette.
(b) the friction caused by separating the first turn of the coiled film in the cassette from the turn below it. When the coiled film is placed in the cassette it tends to clockspring outwards towards the internal wall of the cassette.
(c) the friction caused by overcoming the continual lobing of the film that forms in the area which leads to the exit slot. This lobing is also caused by the film clockspringing.
In the past, attempts have been made to provide cassettes which did not require velvet light sealing lips, for example the cassettes described in British patent specification Nos. 1082488 and 1458819. However in both these cassettes it appears that increased friction was encountered when the film was withdrawn past the light labyrinth. Further, some distortion of the film was also encountered. However it remains a very desirable object to provide velvet-less cassettes not only to reduce friction but also to avoid scratch marks on films as grit particles can easily be caught in the velvet pile and such particles cause a scratch mark on a film whenever the film is pulled past them. Further the placing and adhering of the two pieces of velvet in the slot is cumbersome and involves the use of adhesive which sometimes becomes transferred to the other parts of the cassette.